Development of cataracts, a clouding of the material within the lens capsule of the eye, commonly accompanies the aging process. In response to this routine problem, eye surgeons have developed several techniques for cataract extraction. Generally, cataract extraction involves making an incision through the anterior surface of the lens capsule. Clouded material is removed through suction of the lens nucleus emulsion (phacoemulsification), without removing the entire lens capsule. After surgery, since a portion of the natural lens of the eye has been removed, light entering the eye through the cornea and pupil is unfocused. In order to correct this condition, an artificial intraocular lens is usually implanted directly into the eye after cataract extraction.
An essential step in cataract extraction is the incision of the anterior lens capsule. One current technique for incising the anterior lens capsule, known as capsulotomy, uses a straight intravenous needle with a sharp wedge attached to one end. The wedge is used manually or driven ultrasonically in a chopping motion to perforate the anterior capsule. This technique produces a hole with jagged edges, similar to the edges produced when one opens a can with a manual can opener.
Although this technique has been widely used in conjunction with cataract extractions, it is not entirely satisfactory. The geometry of an incision produced using capsulotomy is unpredictable and susceptible to linear tears. In the worst case, such tears in the capsule can result in the release of the lens nucleus into the vitreous cavity of the eye. Additionally, capsulotomy produces an irregular aperture in the anterior capsule, which may lead to asymmetrical scarring. This condition may allow the implanted intraocular lens to migrate out of the visual axis subsequent to surgery. Additionally, capsulotomy produces a large aperture which allows nuclear lens debris from phacoemulsification to impact the corneal endothelium. Normally, the corneal endothelium keeps the cornea optimally hydrated. Injury to this layer by impacted nuclear debris from phacoemulsification may lead to corneal edema and ultimately an irreversible clouding of the cornea.